In recent years, an electric vehicle, which includes a battery and an electric motor and travels with electric power, is beginning to spread. The electric power needed for the electric vehicle to travel is supplied from the power supply station installed in a public facility or the like and the supplied electric power is stored in the battery of the electric vehicle.
It is proposed in, for example, WO2011/125214A, that the electric power stored in the battery of the electric vehicle is supplied to a building via the power supply station.
When the power supply station and the electric vehicle are connected via a cable and when the electric power is supplied to the electric vehicle (this electric power supply is called herein “charging”) or the electric power is supplied to the building (this electric power supply is called herein “discharging”), it is required to perform communication between the power supply station and the electric vehicle in addition to connecting the power supply station and the electric vehicle via the cable.
For example, in the charging, a signal indicating an upper limit of current may be transmitted from the power supply station to the electric vehicle. A charging permission signal for permitting electric power output may be transmitted from the electric vehicle to the power supply station. Additionally, a signal indicating a connecting state of the cable may be transmitted bidirectionally. A communication method for transmitting these signals is specified as a CPLT (control pilot) communication standard.
With regard to communication between the power supply station and the electric vehicle in the discharging, no standard is specified up to now. WO2011/125214A proposes a concrete example of the communication method in the discharging.